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Masculine facial morphology (e.g., larger jaw, prominent cheekbones) have been linked to a suite of social outcomes—including greater wealth, career progress, romantic desirability, and even greater political success. A leading explanation for these links is that dominant facial structures represent honest cues of physical dominance and fighting ability. Třebický et al. (2013) published the first study to demonstrate that masculine facial cues (e.g., large nose, deep-set eyes) similarly predict both dominance judgments and real-world fighting success, but no studies have replicated these popular findings that a large and specific assortment of masculine facial structures are implicated in both fighting ability and dominance perception. Thus, we conducted a pre-registered direct replication and extension of Třebický et al. (2013). Two separate samples of United States MTurk participants rated 516 UFC fighters' facial photographs on perceived aggressiveness (N = 500) and fighting ability (N = 500). Results showed that perceived aggressiveness was associated with masculine facial morphology (e.g., large nose, deep-set eyes) independent of bodily size. There was also some evidence that perceived fighting ability was associated with masculine facial morphology, which disappeared after controlling for bodily size. There was no support for the relation between facial structure and fighting success, and there were often negative relations between perceived aggressiveness and fighting ability on fighting success (i.e., more successful fighters were perceived as less successful and aggressive). We argue that our evolved psychology differentially processes the distinct avenues to victory that constitute overall fighting success (e.g., knockout versus submission wins). [ABSTRACT FROM AUTHOR]

Methamphetamine (METH) abuse is associated with a spectrum of behavioral consequences, among which heightened aggression presents a significant challenge. However, the causal role of METH's impact in aggression and its target circuit mechanisms remains largely unknown. We established an acute METH exposure-aggression mouse model to investigate the role of ventral tegmental area (VTA) dopaminergic neurons and ventral medial hypothalamus VMH glutamatergic neuron. Our findings revealed that METH-induced VTA dopamine excitability activates the ventromedial hypothalamus (VMH) glutamatergic neurons, contributing to pathological aggression. Notably, we uncovered a dopaminergic transmission within the VTA-VMH circuit that exclusively functioned under METH influence. This dopaminergic pathway emerged as a potential key player in enabling dopamine-related pathological aggression, with heightened dopaminergic excitability implicated in various psychiatric symptoms. Also, the modulatory function of this pathway opens new possibilities for targeted therapeutic strategies for intervention to improve treatment in METH abuse and may have broader implications for addressing pathological aggression syndromes. • Elevated VTA dopaminergic excitability emerges as a key contributor to METH-induced aggression. • Dopamine presence in the VMH is exclusive to METH influence. • The VTA-VMH circuit is engaged, playing a dual role in both the development and modulation of METH-induced aggression. [ABSTRACT FROM AUTHOR]

In semi-natural mixed-sex groups, rabbits (Oryctolagus cuniculus) organize their social life by forming a hierarchy, which is characterized by linearity and stability. Compared to the natural environment, many factors are different in contemporary breeding systems, such as space allowance and, in the case of semi-group housing, a period of single housing around parturition. Aggressive interactions and the resulting injuries are frequently regarded as negative. However, there is not much information about the social dominance among does in these breeding groups. Therefore, the aim of this study was to generate knowledge about the hierarchy in female rabbits kept in "semi-groups" on farms by using sociometric measurements. Sixteen semi-grouped does of three or five rabbits each with various degrees of familiarity were first mixed one week before parturition. After a separation period of either two or three weeks for giving birth, they were remixed with the same group mates. Both mixing procedures were video-analyzed for agonistic interactions. The observed agonistic behavior was mainly characterized by one-sidedness. Mixing rabbits before parturition did not prevent aggression after the separation period. The resulting hierarchies were neither found to be totally despotic nor egalitarian, as linearity was revealed in most groups, but steepness levels varied between them. While dominant does turned out to be rather despotic, showing high win proportions, the other relationships among lower-ranked does were more balanced. In contrast to the stable hierarchical structure in natural breeding colonies, rank order stability was not confirmed in the studied semi-groups. A larger group size negatively influenced the rank stability. Our results point out some characteristics of the social life in semi-grouped rabbit does in contemporary breeding systems and the differences to semi-natural habitats. [ABSTRACT FROM AUTHOR]

• Hamsters show sex differences in the formation of dominance relationships. • Dominance relationships are less stable in female compared to male hamsters. • Dominance status creates sex differences in status-dependent neural plasticity. Dominance relationships are identified by changes in agonistic behavior toward specific individuals. While there are considerable individual and species differences in dominance relationships, sex differences are poorly understood in rodent models because aggression among female rodents is rare. The aim of this study was to characterize sex differences in the formation and maintenance of dominance relationships in same-sex pairs of male and female Syrian hamsters. We pooled data from multiple projects in our lab to evaluate dominance interactions in 68 male dyads and 88 female dyads. In each project, animals were matched with a partner similar in age, sex, and estrous cycle and we exposed animals to daily social encounters for two weeks in a resident-intruder format. We found that female hamsters were quicker to attack and attacked at higher rates compared to males regardless of dominance status. In addition, resident female hamsters were quicker to attack and attacked at higher rates than intruder females, but aggression in males did not depend on residency status. Female subordinates were quicker to submit and fled at higher rates from their dominant counterparts compared to male subordinates. Intruder subordinate females were quicker to submit and fled at higher rates than resident subordinate females. Females were also more resistant than males to becoming subordinate in that they fought back more consistently and were more likely to reverse their dominance status. These findings indicate that dominance relationships are less stable in females compared to males and that residency status has a larger impact on agonistic behavior in females than males. Overall, differences in how males and females display territorial aggression can lead to sex differences in the establishment and maintenance of dominance relationships. [ABSTRACT FROM AUTHOR]

This narrative review article summarizes the current state of knowledge regarding the relationship between the endocannabinoid system (ECS) and aggression across multiple vertebrate species. Experimental evidence indicates that acute administration of phytocannabinoids, synthetic cannabinoids, and the pharmacological enhancement of endocannabinoid signaling decreases aggressive behavior in several animal models. However, research on the chronic effects of cannabinoids on animal aggression has yielded inconsistent findings, indicating a need for further investigation. Cannabinoid receptors, particularly cannabinoid receptor type 1, appear to be an important part of the endogenous mechanism involved in the dampening of aggressive behavior. Overall, this review underscores the importance of the ECS in regulating aggressive behavior and provides a foundation for future research in this area. • Endocannabinoid system plays a role in aggression as demonstrated by pharmacological and genetic manipulations. • Acute activation of cannabinoid receptors reduces aggression in multiple vertebrate species. • Chronic treatment with cannabinoids on animal aggression has yielded inconsistent findings. • Evidence suggests that CB1 receptors play a role in brain process responsible for dampening aggressive behavior. [ABSTRACT FROM AUTHOR]

Abstract Anger may have evolved to orchestrate social bargaining behaviors, which ultimately can lead to establishment of dominance hierarchies. Although the relationship between anger and dominance has strong empirical support, most studies have focused on visual cues of dominance. Across two experiments, we tested the hypothesis that anger increases dominance-seeking and agonistic behaviors in those who feel it. In the first experiment (n = 82), we induced anger through a hostile mock debate and measured corrugator electromyographic activity, testosterone and cortisol levels, status-seeking tendency, and aggression using behavioral tasks. Compared with the control group, the anger group showed higher levels of aggression and status seeking, with the moderator effect of anger intensity. In the second experiment (n = 162), anger, fear, sadness, and neutral state were induced by film clips, after which dominance-related behavioral tendencies were assessed. The anger group showed higher dominance scores, differing significantly from the fear, sadness, and/or control groups. These findings reinforce the notion that feelings of anger can cause an increase in status-seeking and agonistic behaviors, leading to possible action tendencies for the establishment of dominance hierarchies. [ABSTRACT FROM AUTHOR]

The enzyme steroid 5α-reductase 2 (5αR2) catalyzes the conversion of testosterone into the potent androgen 5α-dihydrotestosterone. Previous investigations showed that 5αR2 is expressed in key brain areas for emotional and socio-affective reactivity, yet the role of this enzyme in behavioral regulation remains mostly unknown. Here, we profiled the behavioral characteristics of 5αR2 heterozygous (HZ) and knockout (KO) mice, as compared with their wild-type (WT) littermates. While male 5αR2 KO mice displayed no overt alterations in motoric, sensory, information-processing and anxiety-related behaviors, they exhibited deficits in neurobehavioral correlates of dominance (including aggression against intruders, mating, and tube dominance) as well as novelty-seeking and risk-taking responses. Furthermore, male 5αR2 KO mice exhibited reduced D 2 -like dopamine receptor binding in the shell of the nucleus accumbens – a well-recognized molecular signature of social dominance. Collectively, these results suggest that 5αR2 is involved in the establishment of social dominance and its behavioral manifestations. Further studies are warranted to understand how the metabolic actions of 5αR2 on steroid profile may be implicated in social ranking, impulse control, and the modulation of dopamine receptor expression in the nucleus accumbens. [ABSTRACT FROM AUTHOR]

Social subordination increases risk for psychiatric disorders, while dominance increases resilience to these disorders. Fluoxetine, a selective serotonin (5HT) reuptake inhibitor whose actions are mediated in part by the 5HT1A receptor (5HT1AR), has sex- and social status-specific effects on socioemotional behavior and aggressive behavior. However, the impact of social status on these sex-specific effects remains unclear. The current study evaluated the impact of acute fluoxetine treatment and social status on dominance-related behaviors in female and male hamsters, and the impact of chronic fluoxetine treatment on socioemotional behavior and 5HT1AR binding potential (5HT1AR BP) in female rhesus macaques. We hypothesized that sex differences in the effects of fluoxetine on aggression in hamsters would be diminished in dominant and enhanced in subordinate males and that aggression in female hamsters would be enhanced in dominants and diminished in subordinates. In female rhesus macaques, we hypothesized that chronic fluoxetine would alter socioemotional behaviors and site-specific 5HT1AR BP in a status-dependent manner. Male (n = 46) and female (n = 56) hamsters were paired with conspecifics for three days to establish social rank. Hamsters received a single dose of 20 mg/kg fluoxetine or vehicle two-hours prior to a test with a non-aggressive intruder. Female rhesus monkeys (n = 14) housed were administered fluoxetine (2.8 mg/kg/day) or vehicle injections chronically for 14-days, separated by a three-week washout period. On Day 15, positron emission tomography neuroimaging for 5HT1AR BP was conducted. Fluoxetine treatment decreased aggression in subordinate female monkeys and subordinate female hamsters but not in dominant females of either species. Fluoxetine decreased aggression in dominant but not in subordinate male hamsters. Fluoxetine also reduced and increased prefrontal 5HT1AR BP in dominant and subordinate females, respectively. Taken together, these results provide cross-species evidence that social status and sex impact how increased 5HT modulates agonistic behavior. • Fluoxetine decreased aggression in subordinate female hamsters and monkeys. • Fluoxetine did not impact aggression in dominant females of either species. • Fluoxetine decreased aggression in dominant but not in subordinate male hamsters. • Fluoxetine had opposite effects on prefrontal 5HT1AR in dominant and subordinate female monkeys. • Social status and sex impact how 5HT modulates agonistic behavior across species. [ABSTRACT FROM AUTHOR]

In each population of the livebearing fish Xiphophorus variatus , only a small portion of the adult males develop bright yellow-red (YR) coloration on the dorsal and caudal fins. Here we characterized the dominance hierarchy in X. variatus and tested whether YR coloration is related to a male's position in the hierarchy and can therefore serve as a reliable cue to rival males. Populations varied considerably in the frequency of YR males. Across all populations, males with YR coloration were significantly larger than the rest of the males in the population. Observations of aggressive interactions among males in small groups in the laboratory revealed a sized-based dominance hierarchy with YR males at the top. Aggression was more common among males of a similar size and fighting increased as male body size differences decreased. However, despite the reliability of YR coloration as a signal of dominance status, males at lower social ranks did not avoid aggression with YR males and YR males did not experience fewer aggressive attacks compared to non-YR males. Our findings demonstrate that fin coloration is a reliable cue of a male's social status but rival males appear to not use this information to avoid potentially costly interactions with dominant males, suggesting that YR fin coloration has not evolved as a cue in agonistic interactions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Sex does not influence latency to fight onset and duration in juvenile tilapia. [•] Sex neither influences the aggression types nor intensity in juvenile tilapia. [•] The probability of becoming dominant fish is not influenced by sex in juvenile tilapia. [ABSTRACT FROM AUTHOR]

While an extensive literature has demonstrated that the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine, disrupts aggressive behavior in male Betta splendens the behavioral mechanisms underlying this disruption remain unknown. To elucidate the behavioral mechanism underlying fluoxetine, male fish were acutely exposed to a 10 μmol (0.0034578 μg/L) concentration of fluoxetine for 25 days using an ABA design. Male Betta splendens are naturally aggressive fish with well-studied and patterned behavioral responses. Importantly, aggressive behavior in this species can be conditionally primed allowing for examination of motivational components of behavior in addition to motor performance. The present study focused on using female fish as an ecologically relevant prime for eliciting aggressive behavior as a means of examining the motivational and motoric effects of fluoxetine. We found that male courtship with a female was strongly correlated with aggressive responding against a mirror. However, despite the strong correlation male fish were not found to have different levels of aggression or changes in aggressive responding when compared to males not primed with a female. Also, latency was not different between the no female prime and female prime males for either the excitatory mirror condition or inhibitory white wall condition, of which the fish had no preference. However, fluoxetine was found to have profound effects on all males in the study regardless of prime type, with increases in latency for the mirror and white wall and decreases in aggressive responding to the mirror. These results support the hypothesis that fluoxetine impairs aggressive motivation and movement in Betta splendens. • Male Betta splendens were exposed chronically to fluoxetine using an acute daily dose. • Males exposed to fluoxetine had negative impacts on courting and aggressive behavior. • The female prime did not significantly alter male behavior compared to controls. [ABSTRACT FROM AUTHOR]

Summary: Gonadal hormones mediate both affiliative and agonistic social interactions. Research in estrogen receptor alpha (ERα) or beta (ERβ) knockout (KO) mice suggests that ERα increases and ERβ decreases male aggression, while the opposite is found for female ERαKO and ERβKO mice. Using a detailed behavioural analysis of the resident-intruder test, we have shown that the ERβ selective agonist WAY-200070 increased agonistic behaviours, such as aggressive grooming and pushing down a gonadectomized (gonadex) intruder, in gonadally intact but not gonadex male and female resident mice, while leaving attacks unaffected. The role of acute activation of ERα in agonistic behaviour in adult non-KO CD1 mice is presently unknown. The current study assesses the effects of the ERα selective agonist 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT) on the social and agonistic responses of gonadally intact and gonadex male and female CD1 mice to a gonadex, same-sex intruder. PPT had few effects in gonadally intact mice, but seems to increase sex-typical aggression (i.e., attacks in males, other dominance-related behaviours in females) in gonadex mice. In untreated mice, we confirmed our previous findings that gonadally intact males attacked the intruder more than females, but females spent more time engaged in agonistic behaviour than males. As in our previous results, we observed that gonadex mice generally show behaviour patterns more like those of the gonadally intact opposite sex, while leaving overall levels of agonistic behaviour unaffected. Taken together, our current and previous results show that exogenous activation of ERα had no effects in gonadally intact mice, but increased sex-typical agonistic behaviour in gonadex mice, while ERβ had no effects in gonadex mice, but increased non-attack agonistic behaviour in gonadally intact animals. This suggests that, as in social recognition, ERα may be necessary for the activation of agonistic responses, while ERβ may play a modulatory role. [Copyright &y& Elsevier]

Abstract: Intra and interspecific comparisons of arginine vasotocin (AVT) and its mammalian homolog arginine vasopressin (AVP) demonstrate several relationships between these neuropeptides and aggression/dominance behaviors. Prior studies in coral reef butterflyfishes and other fishes indicate that features of AVT neurons in the gigantocellular preoptic area (gPOA) and axon varicosities within the ventral nucleus of the ventral telencephalon should have a positive relationship with aggressive behavior, whereas AVT-ir neuronal features in the parvocellular preoptic area (pPOA) should have a negative relationship. We measured the offensive aggression of wild caught territorial monogamous multiband butterflyfish, Chaetodon multicinctus, in a simple lab paradigm that controlled for social context and variations in social stimuli. Offensive aggression did not follow a clear stereotyped pattern, but rather a complex sequence that includes five action patterns and two approach behaviors. We then used immunohistochemistry to test for associations between AVT immunoreactive features and projections with overall offensive aggression. Our results indicate that gPOA cell number was positively related to aggression while both the size and number of pPOA cells were negatively related to aggression. No association between aggression and the number of axon varicosities in the telencephalic region proposed to be associated with aggression was found. This study provides further support for the relationship between AVT neuronal features and aggression in fishes, and provides preliminary evidence that this relationship may relate to the motivation to produce aggressive behaviors in the immediate future. [Copyright &y& Elsevier]

Abstract: Although there is compelling evidence for associations between facial masculinity and indices of dominance in men, comparatively few studies have tested for corresponding associations in women. Here we found that (1) ratings of women’s facial masculinity were correlated with their scores on a dominance questionnaire, and (2) prototypes with the average facial characteristics of women with high scores on the dominance questionnaire were judged to be more masculine than prototypes with the average facial characteristics of women with low scores, even when color and texture cues were kept constant to control for effects of makeup use. These findings suggest an association between facial masculinity and dominance in women, complementing prior work reporting that masculine women are perceived to be more dominant than their relatively feminine peers. [Copyright &y& Elsevier]

Summary: Affiliative and agonistic social interactions are mediated by gonadal hormones. Research with estrogen receptor alpha (ERα) or beta (ERβ) knockout (KO) mice show that long-term inactivation of ERα decreases, while inactivation of ERβ increases, male aggression. Opposite effects were found in female αERKO and βERKO mice. The role of acute activation of ERα or ERβ in the agonistic responses of adult non-KO mice is unknown. We report here the effects of the ERβ selective agonist WAY-200070 on agonistic and social behavior in gonadally intact and gonadectomized (gonadex) male and female CD-1 mice towards a gonadex, same-sex intruder. All 15min resident–intruder tests were videotaped for comprehensive behavioral analysis. Separate analyses assessed: (1) effects of WAY-200070 on each sex and gonadal condition; (2) differences between sexes, and between gonadally intact and gonadex mice, in untreated animals. Results show that in gonadally intact male and female mice, WAY-200070 increased agonistic behaviors such as pushing down the intruder and aggressive grooming, while leaving attacks unaffected. In untreated mice, males attacked more than females, and gonadex animals showed less agonistic behavior than same-sex, gonadally intact mice. Overall, our detailed behavioral analysis suggested that in gonadally intact male and female mice, ERβ mediates patterns of agonistic behavior that are not directly involved in attacks. This suggests that specific aspects of aggressive behavior are acutely mediated by ERβ in adult mice. Our results also showed that, in resident–intruder tests, female mice spend as much time in intrasexual agonistic interactions as males, but use agonistic behaviors that involve extremely low levels of direct attacks. This non-attack aggression in females is increased by acute activation of ERβ. Thus, acute activation of ERβ similarly mediates agonistic behavior in adult male and female CD-1 mice. [Copyright &y& Elsevier]

Several lines of theory and research suggest that power (e.g., social dominance) and status (e.g., social prominence and positive peer regard) are enjoyed by those blessed with good looks. The present work addresses the relations among physical attractiveness, power, status, and aggression from a resource control theoretic perspective that suggests that group members find power holders physically attractive, even if they are aggressive. Teacher ratings of physical attractiveness, social dominance, peer reception, aggression, and social skills were collected on 153 preschoolers (3–6 years) from a Midwestern city. Positive peer regard was derived via sociometric nominations. Raters unfamiliar with the children assessed their physical attractiveness from photographs. Results show that teachers'' perceptions of physical attractiveness are a function of power, status, and social skills. Additionally, teachers rated aggressive children who employ both prosocial and coercive strategies of resource control (bistrategic controllers) to be among the most physically attractive. These relations did not emerge for raters unbiased by children''s behavior. Results suggest social dominance achieved via prosocial means begets attractiveness ratings, even if accompanied by high levels of aggression. The implications for intervention are discussed. [Copyright &y& Elsevier]

This study of 61 preschool children used an observational, longitudinal design to examine the degree to which social dominance relationships account for time-related change in rates of aggression and affiliation across a school year. Specific hypotheses reflected the view that, over time, behavioral function should change in accord with the stability of social dominance relationships, social norms, and on-going developmental processes. Results showed that change in rates of aggression was non-linear (i.e., increasing then decreasing over the year), that physical and verbal forms of aggression were associated with distinct longitudinal trajectories, and that these trajectories were related to rates of affiliation and visual regard. As predicted, social dominance accounted for significant variation in these patterns. Implications for theory, future research, and school practitioners are discussed. [Copyright &y& Elsevier]

Immature domestic pigs are increasingly housed in large social groups (>50 pigs) without an understanding of how they adapt to these conditions. At a conventional group size (typically 10–30 animals), pigs exhibit dominance relationships which are frequently established using physical assessments of strength and fighting ability and may include the use of aggressive behaviour. The relationships also rely on individual identification of group members and the recall and reinforcement of previous fight outcomes. This paper reviews the implications of a large group size for the establishment and long-term maintenance of dominance relationships in immature pigs. Evidence suggests that, in large groups, less reliance is placed on aggression during the immediate post-mixing phase than would be expected if the same proportion of dominance relationships are established using aggression in both large and small groups. This occurred despite an ability to distinguish between pen mates and non-pen mates. The energetic costs to a pig of establishing dominance relationships with a given proportion of group members is likely to increase with group size. It is considered whether these elevated costs place a ceiling on the number of fights a pig can engage in or whether they are able to assess dominance ability using passive means and thereby reduce the proportion of group members with which they fight. It is probable that a combination of these two routes is responsible for the limitation of aggression observed. Sub-grouping behaviour, investigated in large poultry groups, appears not to be adopted by pigs in response to a large group size. There is a need for further fundamental research to investigate the way in which pigs adapt behaviourally to a large group size at the level of the individual pig and several potentially fruitful investigations are suggested. [Copyright &y& Elsevier]

Social experience can generate neural plasticity that changes how individuals respond to stress. Winning aggressive encounters alters how animals respond to future challenges and leads to increased plasma testosterone concentrations and androgen receptor (AR) expression in the social behavior neural network. In this project, our aim was to identify neuroendocrine mechanisms that account for changes in stress-related behavior following the establishment of dominance relationships over a two-week period. We used a Syrian hamster model in which acute social defeat stress increases anxiety-like responses in a conditioned defeat test in males and in a social avoidance test in females. First, we administered flutamide, an AR antagonist, via intraperitoneal injections daily during the establishment of dominance relationships in male hamsters. We found that pharmacological blockade of AR prevented a reduction in conditioned defeat in dominant males and blocked an upregulation of AR in the posterior dorsal medial amygdala (MePD) and posterior ventral medial amygdala (MePV), but not in the ventral lateral septum. Next, we administered flutamide into the posterior aspects of the medial amygdala (MeP) prior to acute social defeat stress or prior to conditioned defeat testing in males. We found that pharmacological blockade of AR in the MeP prior to social defeat, but not prior to testing, increased the conditioned defeat response in dominant males and did not alter behavior in subordinates. Finally, we developed a procedure to establish dominance relationships in female hamsters and investigated status-dependent changes in plasma steroid hormone concentrations, estrogen receptor alpha (ERα) immunoreactivity, and defeat-induced social avoidance. We found that dominant female hamsters showed reduced social avoidance regardless of social defeat exposure as well as increased ERα expression in the MePD, but no status-dependent changes in the concentration of plasma steroid hormones. Overall, these findings suggest that achieving and maintaining stable social dominance leads to sex-specific neural plasticity in the MeP that underlies status-dependent changes in stress vulnerability. • Dominant male hamsters show elevated androgen receptors in medial amygdala. • Blocking androgen receptors reduced responses to social defeat in dominant males. • Dominant females show greater estrogen receptor alpha expression in medial amygdala. • Social dominance reduced social avoidance after social defeat stress in females. [ABSTRACT FROM AUTHOR]

• Social stress behavior is similar in mirror, dyad, and altered sign stimulus trials. • Mirror, dyad, and altered sign stimulus trials change the stress type experienced. • Altered stress types change the social experience and neuroendocrine responses. • Altered stress types increase or decrease plasma norepinephrine concentrations. • Altered stress types increase or decrease hippocampal serotonergic activity. Neural and endocrine responses provide quantitative measures that can be used for discriminating behavioral output analyses. Experimental design differences often make it difficult to compare results with respect to the mechanisms producing behavioral actions. We hypothesize that comparisons of distinctive behavioral paradigms or modification of social signals can aid in teasing apart the subtle differences in animal responses to social stress. Eyespots are a unique sympathetically activated sign stimulus of the lizard Anolis carolinensis that influence aggression and social dominance. Eyespot formation along with measurements of central and plasma monoamines enable comparison of paired male aggressive interactions with those provoked by a mirror image. The results suggest that experiments employing artificial application of sign stimuli in dyadic interactions amplify behavioral, neural and endocrine responses, and foreshorten behavioral interactions compared to those that develop among pairs naturally. While the use of mirrors to induce aggressive behavior produces simulated interactions that appear normal, some behavioral, neural, and endocrine responses are amplified in these experiments as well. In contrast, mirror image interactions also limit the level of certain behavioral and neuroendocrine responses. As true social communication does not occur during interaction with mirror images, rank relationships can never be established. Multiple experimental approaches, such as combining naturalistic social interactions with virtual exchanges and/or manipulation of sign stimuli, can often provide added depth to understanding the motivation, context, and mechanisms that produce specific behaviors. The addition of endocrine and neural measurements helps identify the contributions of specific behavioral elements to the social processes proceeding. [ABSTRACT FROM AUTHOR]

Facial width to height ratio (fWHR) has been related to aggression in men in Western samples. This study examined whether fWHR predicted intimate partner violence and dominance in committed relationships in a Chinese sample (n = 144). fWHR was measured in two ways: (1) bizygomatic width divided by the distance between the upper lip and mid-brow and (2) bizygomatic width divided by the distance between the upper lip and highest point of the eyelids. The Conflict Tactics Scale 2 was used to measure intimate partner violence. The 39 items assessed individuals' aggression in five dimensions: (1) negotiation, (2) psychological aggression, (3) physical assault, (4) sexual coercion, and (5) injury. Dominance was measured using the 32-item Dominance Scale where higher scores indicated more dominance. The results found no significant sex differences regarding fWHR. The men that reported a physical assault had larger fWHRs than the men who had no physical assaults. Both fWHRs were positively associated with the men's, but not the women's, physical assault score. Both fWHRs were significantly associated with the disparagement dimension of dominance among the women, but not among the men. The findings indicated the cross-racial consistency of the association between fWHR and aggressive behaviors in multiple situations. [ABSTRACT FROM AUTHOR]

Social behavior is critical for relationship formation and is influenced by myriad environmental and individual factors. Basic and preclinical research typically relies on rodent models to identify the mechanisms that underlie behavior; however, it is important to use non-rodent models as well. A major objective of the present study was to test the hypothesis that biological sex and social experience modulate the expression of social behavior in the adult gray short-tailed opossum (Monodelphis domestica), a non-traditional model. We also investigated the non-associative learning abilities of these animals. Following a period of social isolation, animals of both sexes were paired with a non-familiar, same-sex partner for 10 min on three different occasions, with 24-hour inter-trial intervals. We are the first research group to find significant sex differences in submissive and nonsocial behaviors in Monodelphis. Females displayed significantly higher durations of nonsocial behavior that increased over trials. Males were more aggressive; their latencies to the first attack and submissive behavior decreased over trials whereas these latencies increased for females; males' duration of submissive behavior increased over trials whereas it decreased for females. A different group of subjects habituated in response to repeated presentations to neutral odors and dishabituated in response to novel odors. In addition, both males and females demonstrated the ability to form social memories in a standard individual (social) recognition test. Our results contribute to the characterization of this marsupial species, an important first step in developing it as a model of complex social behaviors. • Biological sex and social experience modulated social behavior in the laboratory opossum (Monodelphis domestica). • Males displayed higher aggression, submission, and open-mouth posture; females displayed more nonsocial behaviors. • Social isolation stimulated male social interest; experience decreased male attack latency and increased it in females. • Males and females habituated/dishabituated to different stimuli, confirming non-associative learning abilities. • Monodelphis , a marsupial species, has great potential to serve as a model of complex social behaviors. [ABSTRACT FROM AUTHOR]